Rocha928

1986S 5-speed will not start and after much analysis I am 95% convinced that the LH-Jetronic has failed and is the cause of no start.

Does anybody have any recommendations (pros/cons) on a company to purchase a rebuilt LH brain from?

Based on my search of Rennlist forum it appears the two main companies providing this service are JDS Porsche and Electronik.

Thanks in advance for feedback and MANY MANY thanks for all the historic Rennlist forum contributors whose technical advice and tips helping solve other member’s car’s problems were invaluable in the diagnoses of my car’s problem!

Lizard928

For LH2.3 (87+)
The rebuilt from JDS is $495 and works with all types of testers.
JDS is also a paid sponsor of this site.

Electronik brains are $650 last I heard, and do not work with some equipment like the sharktuner. Though I cannot confirm this.
They are also not a paid sponsor for this site, and therefor are not allowed to promote their product on here.

Now that said, you have an 1986 with the LH2.2. AFAIK Rich with Electronik does not touch these brains. But I know JDS does have good units. But the LH 2.2 (85-86) rarely fail.

PorKen

Is there someone nearby that can put your LH (and EZF) in their '85-'86.5 to see if it works?

GregBBRD

If you send it in to 928 International, they will test it, for you.

And provide you with a great rebuild, if you need one.

PorKen

LH2² (and EZF) brains are pretty simple inside, with mainly discrete components, and rarely fail.

Buy a (set of) used brain(s) for $200 from eBay, if you are convinced the brain is bad.


For example, if you installed the wrong impedence injectors, it may just be the power transistor for the injectors that needs replacing. Or if you have a bad IAC/ISV, the driver(s) may go out.

John Speake

Suggest you work mehtodically through no-start fault finding.

e.g. check for spark, if no spark change EZ-F relay, the problem might be the CPS but I would swap out with a known good EZ-F first, as they are proving somewhat less reliable than the LH2.2.

If you have spark, and tach flickers when you crank, then change LH relay and also Fuel pump relay.

I do repair LH2.2 and EZ-F if you can't source within the USA at a reasonable price. My prices are very competitive. LH2.2 repairs typically run out much lower price that a LH2.3 rebuild. They are very relaible however. So do check verything else first.

Rocha928

(1986S 5-sp)
Here’s a quick recap of my diagnosis that LH failure likely cause of no start:

Car turns over strong when ignition key is turned, but does not start. Not even a little.

Removed negative battery cable, cleaned it, and reinstalled.

Cannot hear fuel pump when ignition key is turned.

Pulled fuel pump relay, inserted jumper wire, no start.

Swapped fuel pump relay with known working relay from horn. No start.

Swapped LH relay with known working relay form horn. No start.

Attached a portable battery directly to fuel pump using tiny jumper cables, fuel pump ran (buzzed), disconnected portable battery. Sat in car and turned ignition key, car started for 3 seconds then died.

Removed airbox and sprayed either into throttle body, turned key, car started up for 3 seconds then died. Tachometer was active and showed 1,200 to 1,800 during brief engine run.

Please let me know if there is anything else I should try, retry, or try differently. Thanks!

GregBBRD

You are about ten pages of diagnostics from actually needing an LH Brain....

Try leaving the jumper onto the fuel pump, with the separate battery, and see if the thing starts.

If it does, work forward until you find out why there is no power to the fuel pump.

You said nothing about the fuse, BTW.

John Speake

It would be good to know what happened to the car imdediately before the no-start. Was any work done to the car, or did it spontaneously fail to start ?

My experience of LH 2.2 failures is that the most common failure is when someone tries to jump the FPR and they link the wrong pins. This destroys the FP driver stage in the LH.

I think if you correctly jump the fuel pump relay that car will start.

Silverback66

The first rule for the shade tree mechanic: The first thing to check is the last thing you changed.

The second first rule for the shade tree mechanic: Always check all the easy fixes first.

Most often, the solution is easy. Finding the problem can be hard.

Getting both PorKen and John Speake to answer your question is worth more than all those dues you should have paid.

Landseer

And Lizard. And Greg Brown!

Rocha928

Car has been sitting in heated garage for 4 months. Only drove car a few times last year.

Thanks for the suggested things to try. I'll post back hopefully later tonight after I've tried them.

the flyin' scotsman

Did the fuel pump run when the jumper was installed? If so, leave it in place and try to start.

Be extra careful when connecting that external power source to the fuel pump; sparks that close to the fuel tank is not a good situation.

dr bob

Reconnect the portable 12V to the pump, confirm pump is running, and leave the 12V connected as you try to start the car. If the car starts, go after the FP relay, the EZx Relay, the LHx Relay, and check the FP fuse with an ohm meter.

Rocha928

(up date no 1)

Well I took the advice to keep it simple and specific suggestions to re-check fuses, jump the fuel pump relay, and hook-up portable 12-volt battery directly to fuel pump and try to start car with battery connected. I had already done the first two suggestions when I first encountered the no start two weeks back, but I figured what the heck, for once in my life I'll do what I'm told.

To my surprise and questionable confusion, the fuse spot number 42 [fuel pump auxiliary air regulator] was empty??!!! Double checked my count to the 4th spot. Reread fuses panel index. Couldn't believe it or understand why. Still don't. I had already checked all the fuses when I did the horn relay swap two weeks ago.

Pulled 15 amp fuse from complementary driving light spot, tested it in fuse panel's tester, got green light, then stuck in spot 42. Did not yet jump fuel pump relay or hook up battery. Moved over to driver's seat and turned key. Car turned over, pumped gas pedal a little, car did not start, but sounded/felt slightly different. Stopped and paused. Repeated with same result. Tried again and engine started/ran for about 4 seconds. Got kind of smoky so I opened the garage door to air it out. Five minutes later tried again and car started/ran for a few seconds before I turned it off. With garage door and window open, still too much exhaust smoke to continue tonight. Kids in bed and wife in house.

Not sure if car would or would not continue to run. It felt like it might. Will push tail of car outside garage tomorrow and give it a try. Can't wait!

Thanks for everyone's advice and suggestions. Thrilled to perhaps have a fix in hand without an expensive LH rebuilt that potentially would not even have even fixed the no start. Still perplexed on the missing fuse thing and for the life of me cannot figure out any explanation.

Thanks again and I’ll post tomorrow after I give it another try.